Laminitis is a potentially devastating condition which can strike any hoofed animal, but is primarily known to affect equine. Generally speaking, laminitis is a syndrome involving the sensitive laminae of the hoof. The lamina is a layer of loose connective tissue attaching the distal phalanx to the hoof wall.
The syndrome can proceed through several stages, beginning with little or no visible signs of the disease, though lamellar damage may have already occurred at this point. Once begun, if unchecked, the condition can advance to a chronic stage, which can involve detachment of the lamina from the hoof and palmar rotation or even distal displacement of the bone. At the chronic stage, a horse can be left with continuous mild or severe pain which can last indefinitely. It is generally held that the laminitis syndrome is responsible for the permanent debilitation of countless horses every year, affecting all breeds around the world.
While the pathophysiology of the syndrome has gained understanding in recent years, attempts at treatment and prevention of the disease have met with limited success. In the past, treatment was limited to physical treatment of the affected foot, by, for example, minimizing movement by standing the horse in a deep (18 inch) bed of shavings, or fitting special frog supports for the animal. Chemical treatment of symptoms has also been utilized in the past, such as administration of phenylbutazone for inflammation and pain.
More recently, studies have shown that laminitis may begin as a primary vascular disease, and treatment methods have focused on vascular control mechanisms. For example, it has been proposed that digital venoconstriction may be the primary disturbance occurring in the initial stages of laminitis. As a result, certain substances have been examined that may interrupt this process. For example, certain catecholamine antagonists have been examined for possible efficacy. Catecholamines are believed to be mediators in the hormone cascade which can lead to vascular constriction. Specifically, certain xcex1-adrenergic antagonists have been examined as possible agents for inhibiting suspected hormone cascades which can lead to the vasoconstriction found in early laminitis. Success has been limited, however. For example, the xcex1-adrenergic antagonist phenoxybenzamine has been associated with side effects such as hypotension, recumbency, and a prolonged duration of action. Similarly, when the xcex1-adrenergic antagonist acepromazine maleate has been examined, undesirable side effects such as sedation and cholinesterase inhibition can occur in the animal.
In spite of the recent advances in understanding the development of laminitis, specific hormone cascades and possible mediators to the vasoconstriction remain unsubstantiated. Successful treatment of the syndrome remains frustratingly infrequent and uncertain. The present invention is related to a method for treating laminitis and preventing the damage which has been known to occur in the chronic stages of the disease.
In general, the present invention is directed to a method for treating laminitis in animals. More specifically, the present invention is directed to a method for treating the symptoms associated with the laminitis syndrome.
When laminitis proceeds to a chronic stage, laminar detachment can occur, which in turn can lead to palmar rotation and/or vertical displacement of the distal phalanx. The method of the present invention, properly administered, can prevent this laminar detachment.
Laminitis is believed to be due to microcirculatory system impairment. The method of treatment of the present invention includes administering to an animal suffering laminitic symptoms a composition which includes an xcex1-adrenergic antagonist. The xcex1-adrenergic antagonist chosen for treatment is preferably one which does not cross the blood-brain barrier, thus allowing treatment without neuroleptic side effects. In one particular embodiment, the xcex1-adrenergic antagonist can be domperidone.
The xcex1-adrenergic antagonist used for treatment of the animal can be administered to the animal by any suitable method. For example, the xcex1-adrenergic antagonist can be administered to the animal orally, subcutaneoously, or intramuscularly. Generally, the xcex1-adrenergic antagonist will be administered to the animal in an amount from about 0.2 mg to about 3.3 mg per kg weight of the animal. When the treatment is administered to the animal subcutaneously or intramuscularly, the dosage can be, for example, from about 0.08 mg to about 1.32 mg per kg weight of the animal. Administration of treatment can occur at least once per day up to about six times per day (every four hours).
Lamellar damage due to laminitis is known to occur primarily in horses, but it can occur in any hoofed animal. The treatment of the present invention is therefore equally efficacious for other hoofed animals, such as, for example, cattle, camels, goats, pigs, and sheep.
Other objects, features and aspects of the present invention are discussed in greater detail below.
It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary construction.
The present invention is generally directed to treatment of laminitis in hoofed animals. More particularly, the present invention is directed to various processes and methods for treating laminitis and prevention of lamellar damage due to laminitis in animals. The process of the present invention can be used either as a prophylactic for laminitis in hoofed animals or alternatively as a treatment for laminitis after physical manifestations of the disease have appeared. In fact, experimental trials of the treatment have led to long term elimination of any signs of the disease as well as speculation of no return of symptoms in the future.
In general, the objects and advantages of the present invention are achieved by administering to a laminitic animal a composition containing an xcex1-adrenergic antagonist. Preferably, an xcex1-adrenergic antagonist should be chosen that does not substantially cross the blood-brain barrier in order to minimize the possibility of the animal suffering adverse behavioral or neurological side effects. For instance, in a preferred embodiment, the xcex1-adrenergic antagonist is domperidone.
Domperidone is the common name for the compound 5-Chloro-1-[1-[3-(2,3-dihydro-2-oxo-1H-benzimidazol-1-yl)propyl]-4-piperidinyl]-1,3-dihydro-2H-benzimidazol-2-one. Domperidone is registered under the Chemical Abstact Service registration system and has been assigned registry number 57808-66-9. Domperidone is chemically unrelated to other xcex1-adrenergic antagonists, such as phenoxybenzamine and acepromazine maleate. Unlike other xcex1-adrenergic antagonists, domperidone does not cross the blood brain barrier. Therefore, central neurological side effects are not a concern when using domperidone as a treatment for laminitis.
Although a great deal of the pathophysiology of laminitis remains unknown, current research suggests it to be a microcirculatory problem. Current research suggests that prior to lamellar damage, an as yet unknown hormone cascade causes blood vessels to constrict in the distal digit of the animal. It is believed that this constriction involves both pre-capillary bed vessels (arterioles) as well as post-capillary bed vessels (venules). In any case, it is generally held that flow of blood to and/or from the laminar capillaries is impeded in the earliest stages of the disease.
Vasoconstriction which impedes the blood flow in the hoof can cause edema in the surrounding tissues. This in turn can lead to an increase in interstitial pressure which can further impede circulation. The net effect, if left unchecked, can lead to ischemia of the surrounding tissues (including the dermal laminae), formation of thromboses in the vessels, and formation of arteriovenous shunts around the effected area, which further deplete the blood supply to the hoof.
If the disease continues to advance, necrosis of the affected tissue can begin. Sufficient tissue damage can lead to detachment of the laminae from the hoof wall, at which point the phalanx can rotate and/or become vertically displaced within the hoof.
Although the specific hormone cascade which is believed to initiate laminitis is unknown, it is believed to involve catecholamines. Catecholamines are known vasoconstrictive substances and are believed to be intermediaries in the development of laminitis.
In accordance with the present invention, the inventor has discovered that domperidone, properly administered, is a safe and effective treatment for laminitis. Although the specific biological process is unknown, it is believed that domperidone acts as an xcex1-adrenergic antagonist and interferes with the hormone or neurotransmitter cascade with activation of receptors, which can lead to the initial vasoconstriction occurring in the syndrome.
The process of the present invention can be used to treat any animal suffering similar lamellar damage, but is particularly applicable to livestock. For instance, many problems have been experienced due to laminitis in equine, but laminitis exists in other animals as well, such as for example bovine, pigs, sheep, camels, and any other hoofed animal. The disclosed treatment can be used for any laminitic animal.
According to the present invention, the vasoconstriction which is believed to be one of the primary disturbances in early laminitis is inhibited by administering to an animal an xcex1-adrenergic antagonist. In one preferred embodiment, the xcex1-adrenergic antagonist is domperidone. The xcex1-adrenergic antagonist can be administered to the animal in any suitable procedure. For example, the xcex1-adrenergic antagonist can be administered orally, as a subcutaneous injection, as an intramuscular injection, or as a suppository.
In one embodiment, when treating with domperidone, it has been found that laminitic symptoms can be treated when the domperidone is taken orally by an animal in an amount of from about 0.2 mg/kg (mg of domperidone per kg of body weight) to about 3.3 mg/kg. At concentrations greater than 3.3 mg/kg, no further benefits have been observed. Thus far, the best results have been obtained when domperidone has been taken orally at concentrations of about 1.1 mg/kg.
If domperidone is injected subcutaneously or intramuscularly into the animal, the dosages listed above can be reduced to about 40% of the oral dose. Thus, if injected into an animal, domperidone can be administered at a concentration of from about 0.08 mg/kg to about 1.32 mg/kg, with a preferred concentration of about 0.44 mg/kg.
Frequency of administration of the xcex1-adrenergic antagonist can vary from case to case and animal to animal. In general, when treating laminitic symptoms in horses by administration of domperidone, the composition has been found to be effective when administered to the animal at the recommended concentrations at least once per day. In certain embodiments, however, it may be desired to administer the treatment to an animal more often. For example, in some cases, the desired dosage may be administered to an animal about every four hours, or six times per day.
Treatment can begin at the first signs of laminitis. Such signs can include but are not limited to: a pounding digital pulse from the digital artery on either side of the fetlock, pain in the feet, lameness, shifting weight between the feet, hot hooves, standing on the heels, reluctance to move, depression around the coronary band, or frequent lying down. Generally, treatment will continue for several days beyond the termination of symptoms. Should symptoms return, treatment can be reinstituted.
Although unknown, it is believed that xcex1-adrenergic antagonists, such as domperidone, block vasoconstrictor activity within the animal. Domperidone is believed to block xcex1-adrenergic receptors thus neutralizing the effect of certain vasoconstrictive hormones or neurotransmitters like the catecholamines that are believed to be mediators in the hormone cascade leading to the vasoconstriction found in early laminitis.
In general, in delivering an effective dosage of an xcex1-adrenergic antagonist to an animal according to the present invention, various vehicles may be used. For instance, when taken orally, the xcex1-adrenergic antagonist may be combined with a feed or feed supplement material, a suitable oral gel or any other suitable carrier. If injected, the drug may be mixed with any suitable carrier. Additionally, the xcex1-adrenergic antagonist may be added to salt blocks or mineral blocks during casting or mixed directly into feed. Further, various other administration techniques well known in the art may be employed. It is to be understood that the present invention is not to be limited to any particular vehicle.
It also should be appreciated that although the above description and following examples relate primarily to horses, it is believed that the drug will work as described with any animal.
The present invention may be better understood with reference to the following examples.